Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

462
FXUS63 KLOT 052109
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
409 PM CDT Fri Jun 5 2026

.KEY MESSAGES...

- Waves of showers and storms are expected to continue into
  early next week. Many hours will be dry.

- Scattered to numerous storms are likely to occur in the area
  overnight into Saturday morning. The strongest storms tonight
  may be severe and produce torrential downpours.

- Near to slightly above average temperatures are expected this
  weekend before trending warmer next week.

&&

.DISCUSSION...
Issued at 409 PM CDT Fri Jun 5 2026

Through Sunday:

Extensive cloud cover this morning and afternoon prevented
enough destabilization from occurring to support much of a
thunderstorm threat from materializing today, even as a well-
defined MCV passed close by. The bulk of the shower activity
associated with the MCV will continue to peel away to the east
over the next hour, leaving most of our area dry for the
remainder of the afternoon and evening, though the soupy air
mass will still likely support isolated showers lingering
through much of this time frame. Still couldn`t rule out some
lightning occurring during this time frame as well, especially
since equilibrium levels will rise and mid-level lapse rates
will steepen going into this evening as a remnant EML plume is
advected into the area from the west. That said, with forcing
support diminishing with the departure of the MCV, confidence in
lightning occurring through this evening is not particularly
high.

Later tonight, increasing isentropic lift induced by a
strengthening low-level jet will attempt to activate the EML
plume, with ascent likely to be focused near and along a
modified composite outflow boundary that will extend from near
the I-80 corridor in our CWA back westward into southern
Nebraska and northern Kansas. Aided by favorable jet dynamics
aloft, convection is first expected to initiate along this
boundary in the central Plains this evening before spreading
eastward. Between eastward-surging cold pools driving this
convection towards and potentially into our area after midnight
and new cells popping near the surface boundary later on in the
night farther to the east, at least scattered thunderstorms
appear likely occur in our forecast area overnight.

CAM guidance continues to favor the greatest convective
coverage near and south of I-80, which makes sense given the
expected storm motions and initial positioning of the surface
boundary, so have introduced likely PoPs for these areas. That
said, in a true moisture-laden summertime air mass with plenty
of instability aloft like this one, anywhere will ultimately be
fair game for convection to occur, so have kept mid-range
chance PoPs going outside of this more favored corridor for
convection. In addition, another upper-level shortwave trough
tracking through the Upper Midwest could yield a loosely-
organized convective complex that tracks across Wisconsin
tonight. Outflow associated with this complex may tend to
propagate southward and could end up entering northern Illinois
at some point late tonight or early tomorrow morning. If that
does end up occurring, then this outflow boundary could serve as
a focus for convection in our northern locales independent of
what happens farther to the south.

The steeper mid-level lapse rates on the order of 7-7.5 C/km
paired with the existing rich low-level moisture will yield
around 2000-3000 J/kg of MUCAPE across much of our forecast area
well into the night. Deep-layer shear values could vary
considerably with location and time, depending on how far south
the mid-level jet over the Upper Midwest dips and how quickly,
so a messy mix of storm modes is possible. Regardless of the
exact storm mode though, the aforementioned thermodynamic
parameters should support some potential for locally strong to
damaging winds and hail with the more robust convection.
Precipitable water values between 1.25 and 1.75 inches will also
result in torrential rainfall, and the somewhat parallel
orientation of the low-level jet and isentropic forcing with
respect to the aforementioned outflow boundary (or boundaries)
does lend some concern for training convection and localized
flash flooding. That said, the recent dry conditions may tend
to limit this potential to our usual more flood-prone areas.

Any convection that lingers after daybreak on Saturday should
diminish over the course of the morning as the low-level jet
weakens with time. Away from any residual morning cloud cover
and a lake breeze that will push inland, temperatures should
warm solidly into the 80s. The upper 60s-low 70s dew points and
associated instability will hang around for another day, leading
to muggy conditions that could support additional thunderstorm
development later on in the day. A relative lack of large-scale
forcing mechanisms may tend to keep thunderstorm coverage
somewhat limited tomorrow with most locations in our CWA favored
to remain dry, but surface convergence along the lake breeze and
any residual outflow boundaries from the overnight convection
may still prove to be enough for diurnal thunderstorms to fire
in a few areas. MLCAPE approaching 3000 J/kg amidst lackluster
deep-layer shear could support the potential for isolated
strong to damaging wet downbursts with the strongest storms
tomorrow afternoon.

Ogorek


Sunday into Monday:

Toward the start of next week, the upper-level low currently
traversing the US/Mexican border will finally begin lifting
northeastward toward the Mississippi River Valley. The (by this
point somewhat stagnant) humid airmass will hence be poised to
support episodes of showers and storms as the upper-level low
approaches and eventually moves overhead. Periods of cloud
cover, as well as onshore flow forced by a surface high pressure
system moving across eastern Canada, will lead to seasonable
temperatures generally close to 80 degrees both days.


Tuesday Onward:

In the wake of the upper-level low, ensemble model guidance
appears steadfast in depicting the development of persistent
troughing across the Pacific Coast and upper-level ridging
across the Midwest and Great Lakes region. As a result,
temperatures should warm throughout next week with highs
climbing into upper 80s to perhaps lower 90s by the weekend.
When combined with the continued humidity, it`ll start to feel
more like summer next week. Will note that there are differences
in the placement of the ridge next week, suggesting that there
may be opportunities for storms (and associated localized
natural air conditioning) in the general region as well.

(Note that the high temperatures in the mid to upper 90s and
associated much higher heat indices being advertised by the NBM
toward the end of next week are not currently supported by input
ensemble data).

Borchardt


&&

.AVIATION /18Z TAFS THROUGH 00Z SUNDAY/...
Issued at 1232 PM CDT Fri Jun 5 2026

Key Aviation Messages for the current TAF period:

- Occasional SHRA/TS with associated vis reductions through the
  early afternoon

- Another round of showers and storms possible overnight

- Winds switch to the east-northeast tomorrow afternoon with a
  lake breeze

Winds are expected to remain out of the southwest through most
of the TAF window. Gusts around 20 knots are possible through
the afternoon, but will diminish toward sunset this evening.

More impactfully are the shower and storm chances today.
Scattered showers are ongoing, but the short term thunder
trends are down. While the instability is low, it is not zero,
so TAFs were maintained with a PROB30 mention for thunder
through the afternoon. MVFR or locally IFR conditions are
possible during downpours due to a combination of lower cigs
and/or vis.

Lingering showers cannot be completely ruled out this evening,
but models are trending in a break in the rain which results in
not having a mention of it in the TAF. The next wave of showers
and storms is set to develop overnight along and south of a
KSQI to KVPZ line. While the better coverage for thunder is
better south of this line, there remains a PROB30 mention for
the Chicago terminals, with updated timing.

Also overnight, attention is going to be paid to what transpires
in Wisconsin. Models are continuing to develop a cluster of
storms over their area that is expected to move southeastward
toward 12Z. But there is a lot of disagreement in coverage and
track (many have the storms fizzling out by the state line,
others push it out over the lake). While the chances for showers
and storms around KRFD and the Chicago terminals kept the PROB30
in the TAF, these storms could send outflow southward and flip
the winds over to the northeast for a brief period. For now, due
to model uncertainty, any northeast wind mention with the rain
was removed, but will be monitored closely.

Rain chances diminish after 12Z and a return to VFR is expected.
Winds will start out in the morning out of the west, but a lake
breeze is expected to eventually develop in the afternoon
switching the wind directions to the east-northeast.

DK

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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